segment: Pass the interrupt callback on to the chained AVFormatContext, too

This might not be needed at the moment, but it's good practice to
pass it to all chained AVFormatContexts, if it would happen to be
used there at a later point.
Signed-off-by: Martin Storsjö <martin@martin.st>

libavformat/segment.c

@@ -144,6 +144,7 @@ static int seg_write_header(AVFormatContext *s)
         goto fail;
     }
 
+    oc->interrupt_callback = s->interrupt_callback;
     seg->avf = oc;
 
     oc->streams = s->streams;